The present invention is related to apparatus for forming monolithic concrete structures in excavations, particularly full circle cast-in-place pipe or linings.
Elongated monolithic concrete structure forming machines typically embody an inner form that is utilized to progressively form an inner or core surface of the monolithic structure. Concrete is delivered between the excavation walls and the inner form member through a distributor assembly that may be forwardly movable along the length of the inner form. The distributor assembly may be moved forwardly in response to delivery of concrete between the inner form and the excavation walls. It may move forwardly and continuously along the full length of the excavation with the inner form either extending the full length of the excavation or being taken up in sections and placed ahead of the distributor assembly as it progresses forwardly. The distributor assembly typically includes an upwardly facing hopper for receiving concrete. It may also include an oscillating consolidator directly adjacent to the hopper and extending about the inner form structure to increase the fluid flow of concrete about the inner form structure. Various shapes of the finished concrete monolithic structure may be produced by using the distributor assembly and various shapes of inner forms. It is typical to utilize a cylindrical inner form member for formation of continuous concrete pipe.
A serious problem exists in delivering adequate supplies of concrete to the bottom side of the continuous structure, especially during formation of large continuous concrete pipe, culverts or tunnels. Concrete is typically delivered to the hopper at the top of the forming apparatus and must flow downwardly and around an inner form to fill the area between the form and the side walls of the excavation. Even where consolidator mechanisms are utilized to facilitate concrete flow there can be no real assurance that flow of the wet concrete material will completely fill the void between the excavation walls and the inner form at the bottom of the excavation. Insufficient concrete delivery to the area will create holes or depressions within the structure. Excessive flow of concrete to the bottom will cause the apparatus to "float" the inner form, and create excessive wall thickness at the bottom of the structure and misalign the longitudinal axis for the formed structure.
The present invention was conceived to provide an indication as to whether concrete is being received in adequate supplies to the bottom of the excavation, and whether the pressure of the concrete at the bottom is so great as to "float" the inner form.